The at least partly homogeneous operating mode, preferably used for low and medium engine loads, consists in injecting fuel into the combustion chamber very early (for example during the engine intake phase) so as to obtain essentially homogeneous mixing of the fuel with a fluid such as air or a mixture of air and recirculated exhaust gas (EGR).
For the conventional operating mode, preferably used at high engine loads, a fuel injection is performed around the piston compression top dead centre and a conventional combustion by autoignition, then by diffusion occurs.
During this conventional operating mode, it is also possible to carry out a very early fuel injection, for example at the intake phase start.
In the at least partly homogeneous mode, it is advantageous for the fuel injection to occur very early in the engine running cycle in order to obtain an essentially homogeneous mixture, but there are risks of cylinder wall wetting by the fuel injected, leading to a possible oil film deterioration.
Thus, a fuel injection at the start of the intake phase has the advantage of allowing the fuel injected to be confined in the bowl that the piston of such a Diesel engine is usually equipped with, while limiting contact of this fuel with the cylinder wall. However, the temperature of the fluid contained in the combustion chamber is not sufficient and it is therefore difficult for the fuel injected in this bowl, then in the combustion chamber, to vaporize.
In the conventional operating mode, early injection involves the same drawbacks as regards the injected fuel vaporization difficulties and the risks of cylinder wall wetting as those mentioned above.
This fuel vaporization difficulty can lead to disruptions in the progress of the fuel mixture combustion and to an increase in the discharge of pollutants into the atmosphere, as well as fuel overconsumption.
Better fuel vaporization essentially has the advantage of reducing carbon oxides (CO) and unburnt hydrocarbons (HC) emissions upon combustion of the fuel mixture and the soots.
The present invention aims to overcome the aforementioned drawbacks by means of a method using the elements usually present in a direct-injection engine in order to significantly improve vaporization of the fuel when the engine runs according to the at least partly homogeneous mode or during early injection when the engine runs according to the conventional mode.